Female System (Be informed)
The female's reproductive organs lie mainly in the shelter of the pelvis. The opening of her genital tract, the vulva, has two gateways: the outer lips or labia majora, and the inner labia minora. The latter vary considerably in size, and may normally protrude outside the labia majora or be hidden by them.
Both pairs of lips surround a space called the vestibule. This contains the entrance to the vagina - the introitus - and the opening of the urethra, the tube that carries urine from the bladder. Hooded by the junction of the labia minora in front is the clitoris, a small (5 mm) knob of nerve-packed tissue which is the centre of female sexual sensation. In infancy and childhood, the entrance to the vagina is partly closed by a thin membrane, the hymen, which is stretched or broken by the first sexual penetration.
The vagina is a flask-shaped tube, 8-10 cm in length, running upwards and backwards towards the uterus. Its folded lining and the muscle in its wall allow for considerable expansion during intercourse and childbirth. The lining is kept moist by a watery fluid which seeps from capillaries beneath the surface, increasing in amount during sexual arousal.
The vagina meets the uterus at the cervix, the neck or narrowed entrance to the gestation chamber. The uterus, about 7.5 cm long and 5 cm wide, is shaped like an inverted pear. Its strong, muscular walls are about 1 cm thick, and its lining, the endometrium, is specialised for gestation. The uterus is a very mobile organ, being loosely tethered to the pelvic walls by four sets of ligaments. It leans forwards when the rectum is full, backwards when the bladder is full, and can expand up to the diaphragm during pregnancy.
The uterus is joined on either side near the top by the fallopian tubes. These narrow passageways, about 10 cm long, open out in finger-like projections near the surface of the ovary. Their sweeping movements will pickup the ovum as it is released to be transported down the tube to the uterus.
The almond-shaped ovaries have two functions: maturing and release of eggs and production of hormones. At birth the ovaries contain many thousands of ova in a resting, immature state. Each ovum is surrounded by a layer of specialized cells, forming an ovarian follicle. Starting from puberty, the brain begins to order a few of these follicles to develop each month, the instruction being carried by follicle stimulating hormone (FSH) from the pituitary gland. The egg cells begin to mature, and the surrounding cells multiply and start to manufacture the hormone oestrogen. This hormone prepares the female body for pregnancy by stimulating growth of the lining of the uterus and develop and maintenance of all other female secondary sex characteristics. Each month only one of the ripening follicles reaches full maturity. This takes about two weeks, during which time fluid accumulates within the follicle around the ovum. Eventually, increasing amounts of oestrogen produced by the cells of the follicle wall trigger release of luteinizing hormone (LH) from the pituitary. Under the influence of LH the follicle bursts to release the ovum (ovulation), which is captured by the tube to be swept towards the uterus and any sperm that maybe coming the other way.
After ovulation LH directs the remains of the follicle to transform into the corpus luteum, a gland which secretes an additional hormone, progesterone, which halts growth of the endometrium and transforms the uterine lining into a lush secretory layer, rich in blood supply and perfectly designed for implantation of a fertilised ovum. If there is no conception, the corpus luteum degenerates after twelve to fourteen days, oestrogen and progesterone levels fall and the endometrium dies and is shed. This is menstruation. The menstrual discharge consists of the liquefied dead endometrium mixed with some blood which is lost as the tissue breaks down. The usual amount of the menstrual flow is 40-80 ml. This monthly cycle continues from the first period or menarche until the menopause at about 50 years of age.
